Application programs for use on computer-based systems are often distributed on compact discs (CDs) or digital versatile discs (DVDs). DVDs may also be referred to as digital video discs. Generally, the content of entire CDs and DVDs is too large to distribute across the Internet (CDs can store more than 500 MB of data and DVDs are capable of storing more than 4 GB of data). However, many application programs that are distributed on CD or DVD utilize only a small portion of the available storage space on the CD or DVD. If the size of the application program is small enough, pirated copies of the software might be distributed across a network, such as the Internet. To prevent this type of software piracy, it is desirable to determine whether an original CD or DVD (containing the application program) is present in a computing device that is attempting to launch the application.
To determine whether an original CD or DVD is present, an undesirable solution provides a verification system that uses a computer system to compare every byte of data stored on the CD or DVD with a known valid copy of the data stored on the computer system. This solution is undesirable for two reasons. First, the solution requires reading the entire CD or DVD, which is time-consuming. Second, the solution requires storage of a known valid copy of the data on the computer system. Storage of such a large amount of data may not be practical on many computer systems. Further, the required storage space is increased with each new application program that must be verified by the computer system.
Another problem arises when software pirates combine multiple application programs on a single CD or DVD. Since many application programs do not use the entire storage space available on the CD or DVD, software pirates create CDs or DVDs that contain multiple application programs. Although the actual program code may be identical to a legitimate copy of the application program, the excess data stored on the pirated CD or DVD does not match the corresponding lack of data on the legitimate CD or DVD. Thus, it is desirable to provide a verification system that is able to identify otherwise accurate copies of application programs improperly stored on a CD or DVD with other application programs.
Similarly, music is commonly distributed on CDs and, to a lesser degree, on DVDs. The manufacturers of certain music CDs and DVDs may offer additional products or services to customers who purchase music CDs and DVDs. Before offering these additional products or services, the manufacturer must verify that the individual requesting the product or service has obtained a legitimate copy of the original music CD or DVD.
Furthermore, customers purchasing legitimate music CDs and DVDs may use an application program (commonly referred to as a “ripper” application) to extract raw audio data from a CD or DVD and convert the raw audio data to a particular format, such as MP3 (MPEG Audio Layer 3). MP3 is an audio compression technology that compresses CD-quality audio data into music files. MP3 music files are played back on a computer system using an appropriate software program or installed, for example, on a handheld device for playback. To prevent unauthorized copying or distribution of MP3 music files, it is desirable to verify that the user attempting to play or install an MP3 music file has a legitimate copy of the original music CD or DVD.
One solution to this verification problem is to read a particular piece of data from the CD or DVD, such as the volume identifier. The verification system compares the volume identifier read from the CD or DVD to an expected value. If the volume identifier matches the expected value, then the CD or DVD is “verified.” This verification solution is easily defeated by copying the particular piece of data to the appropriate location on the pirated CD or DVD. Thus, a better verification solution is needed to discourage piracy.
As discussed above, attempting to compare every byte of data stored on a CD or DVD with a known valid copy of the data is impractical. The present invention provides a system that verifies the existence of an original data storage medium, such as a CD or DVD, without requiring an analysis of every byte of data stored on the CD or DVD.